Storm drains and inline drains collect storm water and other surface runoff from streets, parking lots, heavily traveled locations, etc. It has become increasingly desirable to have such water drainage undergo some initial cleaning prior to discharge into a receiving water, such as a stream, river, lake, coastal area, or wastewater treatment facility. Many proposals have been made to enhance storm drain effectiveness. Often this is done with the use of a filtration system. For example, U.S. Pat. No. 6,080,307 et al discloses a storm drain with a filter media. These filter media comprise bags with an open structure, and are designed to absorb oils, greases and other hydrocarbons, metals, nutrients, bacteria and sediments from the surface runoff. Gravity pulls the runoff down through the filter media.
With all known runoff treatment systems that use filter media, there has been a problem with buildup of sediment on top of the media when the storm water flows down through the filter media. This downward, gravity forced flow results in clogging of the filter media which leads to reduced flow rates and reduced surface area in the filter media for capturing pollutants. In the treatment of surface water runoff, it would be highly desirable to have a filtration system which did not have this problem.